Particle with 1 GeV mass? I know a proton as a mass of 0.938 GeV also neutron at 0.939.
But I was wondering if there is anything with a measured mass of 1 GeV? Or, whether a proton can have a mass of 1 GeV within a system (as energy has been added), and the rest mass of the system increases?
I have read that "the mass of an isolated proton plus the mass of an isolated electron is slightly different than the mass of the two combined, because their interaction energy affects the mass of the system".
Could this then give a mass of 1 GeV per electron/proton within a system?
 A: 
"the mass of an isolated proton plus the mass of an isolated electron is slightly different than the mass of the two combined, because their interaction energy affects the mass of the system"

Yes, this is true, but unfortunately, when we bring together some particles, and a stable configuration is formed, the system emits what is called binding energy. For instance, bringing together a free electron and a proton, that doesn't make a Hydrogen atom, unless some energy is expelled. Then, we obtain an excited Hydrogen atom, i.e. the electron is on some level, higher than the ground energy level. Even in this case the total energy of the atom is less, not more, than the sum of the energies of the components.
Even if the electron and the proton collide when they have some high kinetic energy, that energy won't get encapsulated in the atom. It would be either passed to center-of-mass energy, or would be simply eliminated in the form of photons. The mass of the Hydrogen atom in the center-of-mass system, and on some energy level of the electron, is one and the same independently of the kinetic energy of the colliding components.
